1. Field of the Invention
The present invention relates to mask evaluating method, mask evaluating system, method of manufacturing mask and computer program product used in a lithography process.
2. Description of the Related Art
As a pattern of semiconductor device is miniaturized, a patterns on the photomask (mask pattern), which is a master of a circuit pattern formed on a wafer is also miniaturize. The micro-fabricated mask pattern requires strict dimension accuracy and defect specifications. For this reason, it is difficult to highly secure a yield of the photomask including the foregoing micro-fabricated mask pattern.
If the yield of the photomask is reduced, a necessity period for manufacturing (manufacture period) the required number of good photomasks becomes longer. The change of the manufacture period gives an influence to the device manufacture planning. For example, the efficiency of development and trial of device is reduced. In order to avoid such a disadvantage, there is need of making a device manufacture plan after predicting the yield of the photomask and estimating the mask manufacture period.
As one of the photomask yield predicting methods, a critical area analysis has been known in the prior art. A description relating to the critical area analysis is disclosed in the JPN. PAT. APPLN. KOKAI Publication No. 2002-100548. The critical area means an area to be a defect which causes a fatal failure such as a short between lines on the wafer if a center of a foreign matter which is dropped on a pattern exist as a defect. This kind of defect to be the fatal failure is called a killer defect.
The method is also applicable to the photomask. That is, the number of killer defects λ and a mask yield Y can be determined from the following definitions using a critical area with respect to a particle size calculated based on mask pattern data of a desired semiconductor product and a defect size distribution calculated based on defect date obtained in step of manufacturing the photomask.λ=∫RAc(R)·D(R)dRY=exp(−λ)
where,
Ac(R): critical area
D(R): defect size distribution
R: defect size
In the defect on the photomask, there exists a defect, which is capable of being saved by defect repair. Therefore, the defect is not regarded as the killer defect. In a case that the method of predicting the yield of the photomask using the conventional critical area analysis (calculation) is performed, the defect capable of being saved by defect repair is determined as the killer defect. For this reason, the difference inevitably occurs between predictive and actual yields. As a method to avoid the case, there is a provided a method of predicting a yield of a mask considering the pattern rescue probability for the defect on the photomask is disclosed in the JPN. PAT. APPLN. KOKAI Publication No. 2003-66590.
Semiconductor devices including kinds of devices are formed on the wafer. These devices include layers. For this reason, the number of kinds of data of photomask required to form all kinds of device on the wafer reaches to the huge value. Usually, some photomasks are only formed for each semiconductor device. That is, the photomask is extremely a large item small volume production. The required precision of the photomask extends wide range from a low required precision to high required precision. Therefore, performing the critical analysis with respect to all mask patterns is not always required and takes lots of analysis time, there is a problem in the photomask production